DEAR DR. BLONZ: My brother and I did genetic tests after precancerous polyps were found during his routine colonoscopy. (Our father died of colon cancer.) Both our genetic tests came back negative for the genes that increase that risk. My brother’s polyps were found at an early stage, so he should be fine, but we are both on regular monitoring programs.
We have changed our lifestyles and eating habits -- being more active and having more fruits, vegetables and fiber. I have grown to like greens such as spinach, but have learned that these and some other vegetables contain nitrates, which can become carcinogenic nitrosamines. This was a bit of a shock. Do these foods need to be avoided, or at least limited? How dangerous are the nitrates in foods? -- S.C., Chicago
DEAR S.C.: It is difficult to learn that one is at increased risk for any cancer. It is good that you and your brother are being proactive with your diet, lifestyle and, of course, the periodic monitoring. These are all associated with decreasing your risk of colon cancer. (Read more about this at b.link/fp2mqb.)
To answer your question, we need to discuss three different compounds: nitrates, nitrites and nitrosamines. Nitrates are naturally present in many different types of foods, including vegetables and fruits. Nitrites are often used as food additives in cured meat products to decrease the risk of botulism. Nitrosamines are carcinogenic compounds that can form when a nitrite combines with an amine. Amines are naturally present in foods, but they are more plentiful when the amino-acid building blocks of a protein get separated during digestion in the small intestine.
For a nitrate to turn into a nitrosamine, it must first be reduced into a nitrite. Once a nitrite, it has to be in close proximity to a specific type of amine in an environment that fosters their combination. Bacteria usually do that conversion of nitrate to nitrite, and while there are bacteria in our saliva, they convert only a small amount of the nitrates we consume. This process is inhibited in an acid environment, so if there is vitamin C in the mix, as there often is with fruits and vegetables, it proceeds even more slowly.
Nitrates tend to be absorbed after they leave the stomach and enter the small intestine. There are bacteria down the road in the large intestine, but by that point, the dangers of nitrate and amine stragglers sidling up to each other and becoming nitrosamines represents a negligible risk.
Contrast all this with nitrite-preserved meat products, in which all the players (the nitrite and amines from the meat protein) are together in the package and throughout their travels in the digestive system. Of course, there is no guarantee that nitrosamines will form, and the use of nitrites to preserve meat products is preferable to the risk of botulism. (Read more on this at medlineplus.gov/botulism.html.)
By comparison, the natural nitrates in fruits and vegetables, including the spinach you now enjoy, represent a walk in the park. So please continue to enjoy these healthful foods.
One other side note: Chronic constipation is a risk factor for colon cancer. Having a healthful lifestyle and a fiber-rich, plant-based, whole-foods diet provides additional help by keeping things moving toward the exit.
Send questions to: “On Nutrition,” Ed Blonz, c/o Andrews McMeel Syndication, 1130 Walnut St., Kansas City, MO, 64106. Send email inquiries to email@example.com. Due to the volume of mail, personal replies cannot be provided.